Hot dip galvanizing protects steel/iron from corrosion by:

(i) It forms a metallic zinc and zinc-iron alloy coating on top of steel surface. This zinc coating reacts with moisture in atmosphere to from zinc salts which act as an insulating layer for steel/iron.

(ii) Zinc is higher than steel/iron in the galvanic series and when these dissimilar metals with different electrical potential are in contact, the zinc anode corrodes and offers sacrificial protection to steel/iron and hence steel/iron is protected from corrosion.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Stainless steel refers to alloy steels with more than 10.5% of chromium and consists of several groups like austenitic, ferritic, martensitic etc. Austenitic stainless steel is normally used in structural applications because of its high corrosion resistance. Austenitic and ferritic types of stainless steel cover about 95% of stainless steel applications. Stainless steel is not stainless although it is corrosion resistant under a wide range of conditions.

A passive layer of chromium oxide is formed on stainless steel’s surface which renders it corrosion resistant. This chromium oxide layer acts as a stiff physical barrier to guard against corrosion and makes it chemically stable. Moreover, when this layer is damaged, it can perform self repairing where there is a sufficient supply of oxygen. However, stainless steel will still corrode by pitting in marine environment where chloride attack occurs.

Therefore, appropriate grades and types of stainless steel have to be selected in polluted and marine environment to minimize the problem of corrosion. Reference is made to Euro Inox and the Steel Construction Institute.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

When structural steelworks are connected to the foundation, pedestals are normally designed to carry loads from metal columns through the ground surface to the footings which are located below the ground surface. With the installation of pedestals, it is the pedestals, instead of metals, which come into contact with soils. The purpose of the provision of pedestals is to avoid the direct contact of metal columns with soils which may cause possible metal corrosion by soils. The soils around the pedestals should be properly compacted to provide sufficient lateral resistance to prevent buckling of pedestals

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

The surface of footings is normally quite rough so that some leveling has to be carried out for the base plates. The interface between the base plates and footings after leveling is subsequently filled with grout.

During grouting, trapping of air may occur at the underside of base plates and this leads to the formation of cavities and uneven contact surfaces on which the base plates are rested. As such, some holes may be drilled in the base plate to avoid the occurrence of air trapping.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

In a typical painting system, there are normally three main layers, primer, undercoat and finishing coat. The primer acts as the first coat of the painting system and adheres to the substrate. It serves to provide a foundation for other coats. The mid-coat, undercoat, is designed to increase the film thickness and hinder the background colour. Moreover, it aids in the reduction of permeability by incorporating pigments like micaceous iron oxide. Finally, the finishing coat contributes to the appearance of the painting system like colour. Sometimes, it may be designed to provide additional abrasive resistance. However, in terms of corrosion protection to steelworks, it does not add much value.

The main component which serves to inhibit corrosion is the primer because it is in direct contact with steel surface. In general the primer is pigmented with inhibitors like zinc and zinc phosphate which protect the steelwork by sacrificial protection. Initially the primer is porous and the products generated by sacrificial protection of zinc fills these voids and the primer acts as a barrier.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.